HLA-DRB1*03:01 is associated with female sex and younger age of anti-LGI1 encephalitis.

BACKGROUND AND PURPOSE: This study was undertaken to investigate the association between human leukocyte antigen (HLA) genotype and clinical characteristics of anti-LGI1 encephalitis. METHODS: HLA genotyping was performed in 34 patients with anti-LGI1 encephalitis admitted to West China Hospital between April 2014 and May 2021, as well as in 305 healthy controls. The online tool NetMHCIIpan 4.0 and AutoDock Vina software were used to predict binding between LGI1 peptide and HLA class II molecules. RESULTS: Risk of anti-LGI1 encephalitis was strongly associated with the DRB1*03:01 allele (odds ratio [OR] = 4.31, 95% confidence interval [CI] = 1.96-9.25, corrected p = 2.75 × 10-4 ) and the DRB1*03:01-DQB1*02:01 haplotype (OR = 4.45, 95% CI = 2.02-9.59, corrected p = 2.94 × 10-4 ). Compared to carriers of the DRB1*07:01 allele, those with the DRB1*03:01 allele were more likely to be female (93.3% vs. 33.3%, p = 0.004) and to be younger (median age = 38 vs. 65 years, p < 0.001). DRB1*03:01 carriers showed stronger response to immunotherapy than carriers of the DRB1*07:01 allele, based on median score decrease on the modified Rankin scale (2, interquartile range = 1-2 vs. 1, interquartile range = 0-1; p = 0.03) at 4 weeks after immunotherapy. Prediction and docking algorithms suggested that the LGI1 peptide can bind to the DRB1*03:01 molecule strongly. CONCLUSIONS: The strong association between anti-LGI1 encephalitis and certain HLA class II alleles supports a primary autoimmune origin for the disease. Carriers of the DRB1*03:01 allele in Chinese patients with anti-LGI1 encephalitis are more likely to be female, to suffer earlier disease onset, and to respond better to immunotherapy.

Role of LGI1 protein in synaptic transmission: From physiology to pathology.

Leucine-Rich Glioma Inactivated protein 1 (LGI1) is a secreted neuronal protein highly expressed in the central nervous system and high amount are found in the hippocampus. An alteration of its function has been described in few families of patients with autosomal dominant temporal lobe epilepsy (ADLTE) or with autoimmune limbic encephalitis (LE), both characterized by epileptic seizures. Studies have shown that LGI1 plays an essential role during development, but also in neuronal excitability through an action on voltage-gated potassium Kv1.1 channels, and in synaptic transmission by regulating the surface expression of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPA-R). Over the last decade, a growing number of studies investigating LGI1 functions have been published. They aimed to improve the understanding of LGI1 function in the regulation of neuronal networks using different animal and cellular models. LGI1 appears to be a major actor of synaptic regulation by modulating trans-synaptically pre- and post-synaptic proteins. In this review, we will focus on LGI1 binding partners, "A Disintegrin And Metalloprotease (ADAM) 22 and 23", the complex they form at the synapse, and will discuss the effects of LGI1 on neuronal excitability and synaptic transmission in physiological and pathological conditions. Finally, we will highlight new insights regarding N-terminal Leucine-Rich Repeat (LRR) domain and C-terminal Epitempin repeat (EPTP) domain and their potentially distinct role in LGI1 function.

Clinical and Prognostic Value of Immunogenetic Characteristics in Anti-LGI1 Encephalitis.

OBJECTIVE: Antibodies against leucine-rich glioma-inactivated 1 (LGI1-Abs) characterize a limbic encephalitis (LE) strongly associated with HLA-DRB1*07:01, although some patients lack LGI1-Abs in CSF or do not carry this allele. Whether they represent a different subtype of disease or have different prognoses is unclear. METHODS: Retrospective analysis of clinical features, IgG isotypes, and outcome according to LGI1-Ab CSF positivity and DRB1*07:01 in a cohort of anti-LGI1 LE patients. RESULTS: Patients with LGI1-Abs detected in both CSF and serum (105/134, 78%) were compared with those who were CSF negative (29/134, 22%). Both groups had similar clinical features and serum levels, but CSF-positive patients had shorter diagnostic delay, more frequently hyponatremia, inflammatory CSF, and abnormal MRI (p < 0.05). Human leukocyte antigen (HLA) genotyping was performed in 72/134 (54%) patients and 63/72 (88%) carried DRB1*07:01. Noncarriers (9/72, 12%) were younger, more commonly women, and had less frequently psychiatric and frontal symptoms (p < 0.05). No difference in IgG isotypes according to CSF positivity or HLA was found (p > 0.05). HLA and IgG isotypes were not associated with poor outcome (mRS >2 at last follow-up) in univariate analyses; CSF positivity was only identified as a poor outcome predictor in the multivariate analysis including the complete follow-up, whereas age and female sex also remained when just the first year was considered. CONCLUSIONS: LE without CSF LGI1-Abs is clinically indistinguishable and likely reflects just a lesser LGI1-Ab production. HLA association is sex and age biased and presents clinical particularities, suggesting subtle differences in the immune response. Long-term outcome depends mostly on demographic characteristics and the intensity of the intrathecal synthesis.

Anti-CASPR2 clinical phenotypes correlate with HLA and immunological features.

OBJECTIVE: Antibodies against contactin-associated protein-like 2 (CASPR2-Abs) have been described in acquired neuromyotonia, limbic encephalitis (LE) and Morvan syndrome (MoS). However, it is unknown whether these constitute one sole spectrum of diseases with the same immunopathogenesis or three distinct entities with different mechanisms. METHODS: A cluster analysis of neurological symptoms was performed in a retrospective cohort of 56 CASPR2-Abs patients. In parallel, immunological features and human leucocyte antigen (HLA) were studied. RESULTS: Cluster analysis distinguished patients with predominant limbic symptoms (n=29/56) from those with peripheral nerve hyperexcitability (PNH; n=27/56). In the limbic-prominent group, limbic features were either isolated (LE/-; 18/56, 32.1%), or combined with extralimbic symptoms (LE/+; 11/56, 19.6%). Those with PNH were separated in one group with severe PNH and extralimbic involvement (PNH/+; 16/56, 28.6%), resembling historical MoS descriptions; and one group with milder and usually isolated PNH (PNH/-; 11/56, 19.6%). LE/- and LE/+ patients shared immunogenetic characteristics demonstrating a homogeneous entity. HLA-DRB1*11:01 was carried more frequently than in healthy controls only by patients with LE (94.1% vs 18.3%; p=1.3×10-10). Patients with LE also had serum titres (median 1:40 960) and rates of cerebrospinal fluid positivity (93.1%) higher than the other groups (p<0.05). Conversely, DRB1*11:01 association was absent in PNH/+ patients, but only they had malignant thymoma (87.5%), serum antibodies against leucine-rich glioma-inactivated 1 protein (66.7%) and against netrin-1 receptor deleted in colorectal carcinoma (53.8%), and myasthenia gravis (50.0%). INTERPRETATION: Symptoms' distribution supports specific clinical phenotypes without overlap between LE and MoS. The distinct immunogenetic characteristics shared by all patients with LE and the particular oncological and autoimmune associations of MoS suggest two very different aetiopathogenesis.

Primary DQ effect in the association between HLA and neurological syndromes with anti-GAD65 antibodies.

The primary cause of neurological syndromes with antibodies against glutamic acid decarboxylase 65 (GAD65-Ab) is unknown, but genetic predisposition may exist as it is suggested by the co-occurrence in patients and their relatives of other organ-specific autoimmune diseases, notably type 1 diabetes mellitus (T1DM), and by the reports of a few familial cases. We analyzed the human leukocyte antigen (HLA) in 32 unrelated patients and compared them to an ethnically matched sample of 137 healthy controls. Four-digit resolution HLA alleles were imputed from available Genome Wide Association data, and full HLA next-generation sequencing-based typing was also performed. HLA DQA1*05:01-DQB1*02:01-DRB1*03:01 was the most frequent class II haplotype in patients (13/32, 41%). DQB1*02:01 was the only allele found to be significantly more common in patients than in controls (20/137, 15%, corrected p = 0.03, OR 3.96, 95% CI [1.54-10.09]). There was also a trend towards more frequent DQA1*05:01 among patients compared to controls (22/137, 16%; corrected p = 0.05, OR 3.54, 95% CI [1.40-8.91]) and towards a protective effect of DQB1*03:01 (2/32, 6% in patients vs. 42/137, 31% in control group; corrected p = 0.05, OR 0.15, 95% CI [0.02-0.65]). There was no significant demographic or clinical difference between DQ2 and non-DQ2 carriers (p > 0.05). Taken together, these findings suggest a primary DQ effect on GAD65-Ab neurological diseases, partially shared with other systemic organ-specific autoimmune diseases such as T1DM. However, it is likely that other non-HLA loci are involved in the genetic predisposition of GAD65-Ab neurological syndromes.

Autoantibodies to synapsin I sequestrate synapsin I and alter synaptic function.

Synapsin I is a phosphoprotein that coats the cytoplasmic side of synaptic vesicles and regulates their trafficking within nerve terminals. Autoantibodies against Syn I have been described in sera and cerebrospinal fluids of patients with numerous neurological diseases, including limbic encephalitis and clinically isolated syndrome; however, the effects and fate of autoantibodies in neurons are still unexplored. We found that in vitro exposure of primary hippocampal neurons to patient's autoantibodies to SynI decreased the density of excitatory and inhibitory synapses and impaired both glutamatergic and GABAergic synaptic transmission. These effects were reproduced with a purified SynI antibody and completely absent in SynI knockout neurons. Autoantibodies to SynI are internalized by FcγII/III-mediated endocytosis, interact with endogenous SynI, and promote its sequestration and intracellular aggregation. Neurons exposed to human autoantibodies to SynI display a reduced density of SVs, mimicking the SynI loss-of-function phenotype. Our data indicate that autoantibodies to intracellular antigens such as SynI can reach and inactivate their targets and suggest that an antibody-mediated synaptic dysfunction may contribute to the evolution and progression of autoimmune-mediated neurological diseases positive for SynI autoantibodies.

[Clinical analysis of 9 cases with Anti-leucine-rich glioma inactivated 1 protein antibody associated limbic encephalitis].

Objective: This study was to describe the clinical characteristics of Anti-leucine-rich glioma inactivated 1 protein(LGI1) antibody associated limbic encephalitis. Methods: Clinical data including clinical features, laboratory and radiological findings, treatment and prognosis of the 9 patients were analyzed. Results: In all 9 cases, 6 cases experienced epileptic seizure, 5 cases had psychosis, 7 cases presented with memory impairment, 4 cases showed faciobrachial dystonic seizure, 2 had refractory hyponatremia. One case presented with typically acute Guillain-Barre syndrome (GBS). Anti-LGI1 antibody was detected in 6 cases in cerebrospinal fluid (CSF) samples and 9 in serum samples. Seven cases out of 9 had brain imaging abnormalities. All 9 cases found no evidence of tumors. Eight cases were given immune therapy. During a 1-16 months follow-up, 1 case had complete recovery, 5cases had various degree of sequelae , among whom 4 had memory disturbance and 1 case had changed personality. 2cases were lost to follow-up. Conclusions: Limbic encephalitis is the most common manifestation of anti-LGI1 antibody associated encephalitis. Faciobrachial dystonic seizure (FBDS) is a specific symptom which favors an early diagnosis. Tumor is uncommon to see. The disease has a relatively favorable prognosis while impaired memory can be seen as a common sequelae.

[THE ROLE OF AUTOANTIBODIES TO THE EXTRACELLULAR REGIONS OF IONOTROPIC RECEPTORS IN ETIOLOGY AND PATHOGENESIS OF AUTOIMMUNE DISEASES].

In the last years it was shown that autoantibodies to the extracellular regions of the ionotropic receptors, such as glutamate AMPA- and NMDA-receptors, GABAA-receptors, glycine and nicotinic acetylcholine receptors, induce a wide spectrum of autoimmune diseases, including limbic encephalitis, Rasmussen's encephalitis, systemic lupus erythematosus, myasthenia gravis, encephalomyelitis, and stiff-man syndrome. In the review the literature data concerning the autoimmune processes provoking autoantibodies formation to the ionotropic receptors, the epitopes participating in the induction of pathogenic autoantibodies, and the effects of these antibodies on the functions of nervous cells and their role in the development of autoimmune diseases were analyzed and systematized. The possible role of oncology diseases in the generation of autoantibodies to the ionotropic receptors was discussed. Approaches that are currently being developed to inhibit the synthesis of pathogenic autoantibodies and to their neutralization were considered. These approaches may be subsequently used to treat the autoimmune diseases caused by the antibodies to ionotropic receptors.

Espectro clínico y valor diagnóstico de los anticuerpos contra el complejo proteico asociado a canales de potasio / Clinical spectrum and diagnostic value of antibodies against the potassium channel related protein complex

Introducción: Los anticuerpos contra un complejo proteico que incluye a los canales de potasio dependientes de voltaje (CKVD) se han descrito en pacientes con encefalitis límbica, hiperexcitabilidad del nervio periférico, síndrome de Morvan, así como en un creciente grupo de síndromes neurológicos. Desarrollo: En este artículo revisamos los síndromes asociados a anticuerpos contra proteínas relacionadas con los CKVD y los 2 antígenos principales de este complejo, las proteínas leucine rich glioma inactivated protein 1 (LGI1) y contactin-associated protein-like 2 (Caspr2). Así mismo describimos los problemas conceptuales y las implicaciones diagnósticas de la descripción de anticuerpos contra CKVD diferentes de LGI1 y Caspr2. Aunque inicialmente se consideró que existían anticuerpos dirigidos contra CKVD, recientemente se ha identificado que, en la mayor parte de los casos, los antígenos son una proteína neuronal secretada denominada LGI1, involucrada en el control de la excitabilidad sináptica, y la proteína Caspr2, localizada en la superficie neuronal de varias regiones cerebrales y en la región yuxtaparanodal de axones mielinizados. Mientras que los anticuerpos contra LGI1 se asocian preferentemente a un cuadro clásico de encefalitis límbica, los anticuerpos contra Caspr2 muestran un espectro clínico más amplio, incluyendo el síndrome de Morvan, la hiperexcitabilidad del nervio periférico o neuromiotonía, o una encefalitis límbica o difusa. Existen además casos descritos de pacientes con anticuerpos contra el complejo CKVD que no tienen anticuerpos contra LGI1 o Caspr2. En estos casos, la identidad y la localización de los antígenos es desconocida, la asociación sindrómica inespecífica y la respuesta al tratamiento, incierta. Conclusiones: El descubrimiento de los antígenos LG1 y Caspr2 ha permitido delimitar clínica y molecularmente el amplio grupo de síndromes previamente atribuidos a anticuerpos contra CKVD. Frente a la literatura que describe la presencia de anticuerpos contra CKVD diferentes a LGI1 y Caspr2, proponemos un algoritmo práctico para el diagnóstico y el tratamiento de estos pacientes

Introduction: Antibodies against a protein complex that includes voltage-gated potassium channels (VGKC) have been reported in patients with limbic encephalitis, peripheral nerve hyperexcitability, Morvan's syndrome, and a large variety of neurological syndromes. Review summary: In this article, a review is presented of the syndromes associated with antibodies against VGKC-related proteins and the main antigens of this protein complex, the proteins LGI1 (leucine rich glioma inactivated protein 1) and Caspr2 (contactin-associated protein-like 2). The conceptual problems and clinical implications of the description of antibodies against VGKC-related proteins other than LGI1 and Caspr2 are also discussed. Although initial studies indicated the occurrence of antibodies against VGKC, recent investigations have shown that the main antigens are a neuronal secreted protein known as LGI1 which modulates synaptic excitability, and a protein called Caspr2 located on the cell surface and processes of neurons of different brain regions, and at the juxtaparanodal region of myelinated axons. While antibodies against LGI1 preferentially associate with classical limbic encephalitis, antibodies against Caspr2 associate with a wider spectrum of symptoms, including Morvan's syndrome, peripheral nerve hyperexcitability or neuromyotonia, and limbic or more extensive encephalitis. In addition there are reports of patients with antibodies against VGKC-related proteins that are different from LGI1 or Caspr2. In these cases, the identity and location of the antigens are unknown, the syndrome association is not specific, and the response to treatment uncertain. Conclusions: The discovery of antigens such as LGI1 and Caspr2 has resulted in a clinical and molecular definition of the broad group of diseases previously attributed to antibodies against VGKC. Considering the literature that describes the presence of antibodies against VGKC other than LGI1 and Caspr2 proteins, we propose a practical algorithm for the diagnosis and treatment of these patients

Limbic encephalitis with anti-GAD antibodies and Thomsen myotonia: a casual or causal association?

The association between hereditary myotonic disorders and epilepsy is seldom described in the literature. To date, few reports have dealt with dystrophic myotonias, whereas a single case demonstrating an association between sporadic congenital myotonia and epilepsy was recently reported in a patient carrying a de novo mutation of the CLCN1 gene. Additional evidence for a role of CLCN1 in the pathogenesis of epilepsy is derived from large-scale exome analysis of ion channel variants and expression studies. Here, we describe the first case of association between familial Thomsen myotonia and epilepsy. All the affected members of a two-generation family presented myotonia and disclosed a pathogenic mutation in CLCN1. In addition, one individual experienced epileptic seizures due to limbic encephalitis (LE) with anti-GAD antibodies. The occurrence of the two diseases in this patient could be a chance association, however, CLCN1 mutation, as a susceptibility factor for epilepsy through dysfunction of GABAA inhibitory signalling, cannot be ruled out as a possible influence.

LGI proteins in the nervous system.

The development and function of the vertebrate nervous system depend on specific interactions between different cell types. Two examples of such interactions are synaptic transmission and myelination. LGI1-4 (leucine-rich glioma inactivated proteins) play important roles in these processes. They are secreted proteins consisting of an LRR (leucine-rich repeat) domain and a so-called epilepsy-associated or EPTP (epitempin) domain. Both domains are thought to function in protein-protein interactions. The first LGI gene to be identified, LGI1, was found at a chromosomal translocation breakpoint in a glioma cell line. It was subsequently found mutated in ADLTE (autosomal dominant lateral temporal (lobe) epilepsy) also referred to as ADPEAF (autosomal dominant partial epilepsy with auditory features). LGI1 protein appears to act at synapses and antibodies against LGI1 may cause the autoimmune disorder limbic encephalitis. A similar function in synaptic remodelling has been suggested for LGI2, which is mutated in canine Benign Familial Juvenile Epilepsy. LGI4 is required for proliferation of glia in the peripheral nervous system and binds to a neuronal receptor, ADAM22, to foster ensheathment and myelination of axons by Schwann cells. Thus, LGI proteins play crucial roles in nervous system development and function and their study is highly important, both to understand their biological functions and for their therapeutic potential. Here, we review our current knowledge about this important family of proteins, and the progress made towards understanding their functions.

[Antibody-associated diseases of the gray matter of the CNS: diagnosis and treatment]. / Antikörperassoziierte Erkrankungen der grauen Substanz des ZNS : Diagnostik und Therapie.

In the past 10 years, the diagnosis and understanding of immune-mediated diseases of the gray matter of the CNS have greatly advanced with the discovery of autoantibodies in serum and CSF of affected patients. The newly described antibodies against neuronal surface antigens, i.e., receptors, channels, and associated proteins, seem to have a direct pathogenic effect on CNS neurons. Fortunately, there is a beneficial effect of immunotherapy in many patients. The diagnosis of autoantibody-associated disease of the CNS gray matter requires the combination of a typical clinical syndrome or a characteristic paraclinical finding (MRI, CSF, histopathology) with the detection of a specific antibody. In the following, an overview will first be given of the syndromes typically associated with autoantibodies. Thereafter, the diagnosis of these syndromes is discussed, and finally, preliminary treatment recommendations are given.

Investigation of LGI1 as the antigen in limbic encephalitis previously attributed to potassium channels: a case series.

BACKGROUND: Voltage-gated potassium channels are thought to be the target of antibodies associated with limbic encephalitis. However, antibody testing using cells expressing voltage-gated potassium channels is negative; hence, we aimed to identify the real autoantigen associated with limbic encephalitis. METHODS: We analysed sera and CSF of 57 patients with limbic encephalitis and antibodies attributed to voltage-gated potassium channels and 148 control individuals who had other disorders with or without antibodies against voltage-gated potassium channels. Immunohistochemistry, immunoprecipitation, and mass spectrometry were used to characterise the antigen. An assay with HEK293 cells transfected with leucine-rich, glioma-inactivated 1 (LGI1) and disintegrin and metalloproteinase domain-containing protein 22 (ADAM22) or ADAM23 was used as a serological test. The identity of the autoantigen was confirmed by immunoabsorption studies and immunostaining of Lgi1-null mice. FINDINGS: Immunoprecipitation and mass spectrometry analyses showed that antibodies from patients with limbic encephalitis previously attributed to voltage-gated potassium channels recognise LGI1, a neuronal secreted protein that interacts with presynaptic ADAM23 and postsynaptic ADAM22. Immunostaining of HEK293 cells transfected with LGI1 showed that sera or CSF from patients, but not those from control individuals, recognised LGI1. Co-transfection of LGI1 with its receptors, ADAM22 or ADAM23, changed the pattern of reactivity and improved detection. LGI1 was confirmed as the autoantigen by specific abrogation of reactivity of sera and CSF from patients after immunoabsorption with LGI1-expressing cells and by comparative immunostaining of wild-type and Lgi1-null mice, which showed selective lack of reactivity in brains of Lgi1-null mice. One patient with limbic encephalitis and antibodies against LGI1 also had antibodies against CASPR2, an autoantigen we identified in some patients with encephalitis and seizures, Morvan's syndrome, and neuromyotonia. INTERPRETATION: LGI1 is the autoantigen associated with limbic encephalitis previously attributed to voltage-gated potassium channels. The term limbic encephalitis associated with antibodies against voltage-gated potassium channels should be changed to limbic encephalitis associated with LGI1 antibodies, and this disorder should be classed as an autoimmune synaptic encephalopathy. FUNDING: National Institutes of Health, National Cancer Institute, and Euroimmun.

CRMP5 antibodies found in a patient with limbic encephalitis and myasthenia gravis.

Collapsin response mediator protein 5 (CRMP5) antibodies are often associated with thymoma or small cell lung cancer and paraneoplastic syndromes such as limbic encephalitis (LE). A patient is described with myasthenia gravis who, following thymectomy and immunosuppression, acquired a viral infection and developed LE and increased levels of serum CRMP5 antibodies. The cognitive symptoms improved and CRMP5 antibody levels decreased after plasma exchange, suggesting that CRMP5 antibodies may have contributed to the development of LE.

Role of IFN-gamma in an experimental murine model of West Nile virus-induced seizures.

Seizures are a major complication of viral encephalitis. However, the mechanisms of seizure-associated neuronal dysfunction remain poorly understood. We report that intranasal inoculation with West Nile virus (WNV) (Sarafend) causes limbic seizures in C57BL/6 mice, but not in interferon (IFN)-gamma-deficient (IFN-gamma-/-) mice. Both strains showed similar levels of virus in the brain, as well as similar concentrations of the cytokines, tumor necrosis factor and interleukin-6, both of which can alter neuronal excitability. Experiments in chimeric IFN-gamma-/- mice reconstituted with IFN-gamma-producing leukocytes showed that IFN-gamma is not required during central nervous system infection for limbic seizure development, suggesting a role for IFN-gamma in the developing brain. This was supported responses to pentylenetetrazole, kainic acid (KA), and N-methyl-d-aspartate (NMDA). Both strains of mice exhibited similar behavior after pentylenetetrazole challenge. However, while NMDA and KA treatment resulted in characteristic seizures in C57BL/6 mice, these responses were diminished (NMDA treatment) or absent (KA treatment) in IFN-gamma-/- mice. Furthermore, NMDA-receptor blockade with MK-801 in WNV-infected C57BL/6 mice abrogated seizures and prolonged survival. Our data show that IFN-gamma plays an important role in the development of the excitatory seizure pathways in the brain and that these cascades become pathogenic in encephalitic WNV infection.